A liquid crystal display includes a backlight unit on the back of a liquid crystal panel for displaying an image for lighting the liquid crystal panel from the back to clearly display the image displayed on the liquid crystal panel. The backlight units are roughly classified into those called an edgelighting type and those called a just-beneath type. The backlight unit of the edgelighting type has a cold cathode fluorescent lamp (CCFL) arranged facing an end face of a light guide plate, in which light incident from the end face is reflected more than once in the light guide plate and light is emitted from the surface of the light guide plate, passes through an optical film, and then is incident on the liquid crystal display panel. On the other hand, the backlight unit of the just-beneath type is made up of a plurality of cold cathode fluorescent lamps arranged in parallel, a reflecting plate provided on the back of the cold cathode fluorescent lamp, a light diffusion plate forming a light emission surface, and an optical film (lens sheet) in combination, wherein light emitted from the surface of the light diffusion plate is passed through the optical film and then is made incident on the liquid crystal display panel. The backlight unit of the just-beneath type can increase the use number of light sources in contrast to the backlight unit of the edgelighting type and thus the light emission surface can be easily put into higher luminance.
Consequently, use of an LED as a light source by adopting the just-beneath type is also proposed for a backlight unit for lighting a liquid crystal panel of a large screen installed in a large-sized electronic machine (see Patent Documents 1 and 2).
The backlight unit of the just-beneath type using LEDs uses LEDs for emitting red light, green light, and blue light of the three primary colors of light as light sources and mixes red light, green light, and blue light emitted from the LEDs to generate white light. Thus, a backlight unit includes a light source section 15 having red LEDs 11R, green LEDs 11G, and blue LEDs 11B arranged alternately in the XY direction on a printed wiring board (PWB) 13, as shown in FIG. 26.
The backlight unit 17 first emits red light, green light, and blue light from the red LEDs 11R, the green LEDs 11G, and the blue LEDs 11B respectively included in the light source section 15 as the sectional structure of the backlight unit 17 shown in FIG. 27. The red light, the green light, and the blue light emitted from the LEDs 11 are naturally mixed into white light while proceeding in the direction in which a diffusion plate 19 and a diffusion sheet 21 are provided, and the light is made incident on a prism sheet 23. The light emitted from the prism sheet 23 lights a liquid crystal panel.
In the backlight unit 17 of the just-beneath type using the LEDs in the related art described above, the red light, the green light, and the blue light emitted from the LEDs 11 are naturally mixed into white light while proceeding in the direction in which the diffusion plate 19 and the diffusion sheet 21 are provided because the luminance distribution of the emission light disperses isotropically.
However, some liquid crystal panels have a liquid crystal light transmission characteristic that the red light, the green light, and the blue light emitted from the LEDs 11 differ in light transmittance in a polar angle direction (slanting direction) inclined at a predetermined angle with respect to the normal perpendicular to a display surface, caused by an optically-compensatory film. Thus, when observing the display surface of the liquid crystal panel from the slanting direction, the colors are not uniformly mixed and there is a problem in that coloration or tinting, which does not occur from the front direction, occurs, namely, a problem of occurrence of viewing angle dependency of tint.
In recent years, with an increase in the size of the liquid crystal display, in particular, in a state where black is displayed, light leakage tends to conspicuously occur at the upper, lower, left, and right ends or at the four corners of a display screen. For this reason, light may leak in a specific visual field direction regardless of the display screen, and in a large liquid crystal display, and deterioration of display quality may be conspicuous.    Patent Document 1: JP-A-2005-327682    Patent Document 2: JP-A-2005-249942